The present invention relates to a video signal transceiver for transmitting and receiving video signals using a transmission line, in particular to video signal transceivers for transmitting video and control signals between a video camera and a base station.
Professional television broadcast cameras for studio and electronic film productions today use either an optical fibre or a special coaxial cable, referred to as a triax cable, for communicating with a base station where image data from one or more cameras are collected and processed. Triax transmission technology has been on the market for a long time, so that in many facilities where professional video cameras are used, for example in sport stadiums, triax cables are installed. A producer who uses triax transmission technology for recording an event can therefore bring his cameras to such a facility, install his base station, and can interconnect cameras and base station using triax cables that are already present on the location.
In order to transmit a video signal from the camera to the base station and a variety of control and feedback signals as well as operating power from the base station to the camera on a single transmission line, triax transmission technology has to use quite sophisticated and expensive interface electronics. The upcoming of high definition television (HDTV) has increased the need for bandwidth on the transmission line between camera and base station still further. It was believed that triax cables would no longer be able to meet this demand.
A particular problem is the attenuation of high frequency signal components on a triax cable. A standard definition television signal can be transmitted on a triax cable over approx. 3 km without suffering from a too serious degradation of quality. For transmitting a HDTV signal, higher frequencies have to be used, so that the loss of quality from attenuation is more pronounced, and the maximum useable length of the cable decreases to about 1500 m.
In view of these problems, it has been proposed to replace the triax cable by optical fibres, and camera and base station interfaces have been developed therefore. Specifically, US 2003/0112338 A1 discloses a television production system in which a camera outputs a baseband television signal, which is converted to an optical signal in a transceiver, which is removably connected to the camera and is adapted to communicate with a base station using an optical fibre cable.
Users have been reluctant to accept this new technology because of the lack of optical fibres installed in the field. While a producer who uses triax technology can in many places use pre-installed cables and thus save a lot of cost and labour, a user of optical fibre technology will often have to do the wiring before he can start an recording event.
This leaves the user in a dilemma. Although from the technical point of view, optical transmission technology is superior to triax because it does not suffer from bandwidth and range limitations as explained above, interfacing circuitry may be simpler than for triax, and cables may be cheaper, early adopters of this technology are confronted with problems because pre-installed optical cables are not available at many locations.
It might be contemplated to complement the system of US 2003/0112338 A1 by adding a triax transceiver, which can replace the optical transceiver in case of need. Still, a user must then have both transceivers in order to have a free choice between using triax or optical cables. This requires an additional investment. Further, the number of components and, hence, the overall weight of the system increases undesirably.